1. Field of the Invention
The present invention relates to an apparatus which performs an intended function by using a fluid whose apparent viscosity varies with an electric current applied thereto. More specifically, the present invention is concerned with a technique for limiting an increase in a current consumed by a power source for the current, which is caused by lowering of a resistance value of the fluid when the fluid temperature is elevated, in order to protect the power source and other peripheral equipments.
2. Discussion of the Prior Art
There is known a so-called electro-rheological fluid or electro-viscous fluid, whose apparent viscosity varies depending on the presence or absence of an electric field applied thereto, or on a magnitude of the electric field. In recent years, such a fluid is employed in various kinds of apparatus, such as a vibration-absorbing system, shock absorber, fluid valve or actuator, in which the viscosity of the fluid is changed as desired by controlling a voltage to be applied thereto. Thus, the apparatus as indicated above is intended to perform various functions by utilizing the characteristic of the fluid. The fluid having the above-described characteristic will be hereinafter referred to as "electro-viscous fluid" when appropriate.
In the apparatus using the electro-viscous fluid, a pair of electrodes are disposed so as to apply an electric current to a mass of the fluid which is present between the electrodes, so that the viscosity of the fluid is changed by controlling a voltage to be applied between the electrodes. However, it is generally recognized that an electrical resistance value of the electro-viscous fluid is suddenly lowered to a great extent when the temperature of the fluid is elevated, whereby the current density of the fluid is increased and the fluid itself generates heat to further elevate the temperature thereof. Consequently, the apparatus suffers from extreme increase in a current cunsumed by the fluid mass or its power source, due to the thus continuously increased temperature of the fluid and the accordingly lowered resistance value of the fluid. In the apparatus in which the temperature of the fluid is likely to be elevated during its use, therefore, the current consumed by the power source is almost unlimitedly increased with the temperature rise of the fluid, resulting in an overloaded state of the power source, and an adverse influence on the power source itself and its peripheral equipments.